Luminescent materials



United States Patent Ofifice 3,163,608 LUMINESCENT MATERIALS Perry N. Yocom, Princeton, N.J., assignor to Radio orporation of America, a corporation of Delaware No Drawing. Filed Apr. 6, 1962, Ser. No. 185,530 Claims. (Cl. 252-3011) This invention relates to novel luminescent materials which are particularly, but not necessarily exclusively, useful as laser materials.

Laser materials and systems are described by Vogel et al. in Electronics October 27, 1961, pages 40 to 47. The word laser is a short form for light amplification by stimulated emission of radiation. Laser materials are luminescent materials which exhibit stimulated emission of radiation under a particular set of conditions. a material exhibits a stimulated emission of radiation, it is said to lase. A laser material is usually a single crystal body of a matrix material having impurity ions or dopants contained therein. The desirable characteristics of a laser material result from the combination of matrix ma-. terial, dopant and crystallinity of the material.

An object of this invention is to provide novel luminescent materials.

A further object is to provide novel laser materials.

In general, the luminescent materials of the invention have the molar composition:

AHa yM where:

A is at least one of Ba, Ca, and Sr Ha is at least one of Cl, Br, and I M is at least one of Sm, Tm+ and U+ y is between about and 10* mol When excited with suitable radiant energy, the foregoing materials luminesce, emitting radiation, generally in the red and infrared regions of the spectrum. This luminescence occurs with the material at room temperature and at liquid nitrogen temperatures. The materials containing a high proportion of barium luminesce in narrow bands at both room and liquid nitrogen temperatures. The materials containing a high proportion of calcium and/ or strontium emit in narrow bands at liquid nitrogen temperatures and in relatively broad bands at room temperature. The wavelength ranges of emitted radiation is related to the dopant. For divalent Samarium Sm, the range is about 5500 to 8500 A. For trivalent uranium U, the range is about 6000 to 25,000 A. For divalent thulium Tm, the range is about 10,000 to 12,000 A. Generally, the emission bands are shifted toward the shorter wavelengths when higher molecular weight A and Ha are selected. When the materials of the invention are prepared in single crystal form with high purity and crystallinity, some or all of the crystals can be made to lase with radiant excitation.

The following are some typical luminescent compositions of the invention:

BaBr 0.01U+ BaBr :0.00004U+ BaBrCl: O.0OlU+ BaCl :0.01Sm+ BaCl :0.lSm+ BaC1I:0.0007Sm+ lBaBrI:0.00lTm' os orz) 10.003Sm+ (Ba Sr )ClBr:0.00lSm+ (Ba Ca Br 0.0007Tm+ CaCl :0.0lSm+ CaCl 0.00001Sm+ CaBr :O.001Tm+ Cal :0.001U+ When . preparation.

MHa are fused together in a reducing atmosphere such as hydrogen or a neutral atmosphere, such as nitrogen, argon, neon, or combinations thereof. The dopant may be introduced as an oxide of M provided the atmosphere contains also the corresponding hydrogen halide. The melt is then solidified by cooling to room temperature in the atmosphere. The AHa may be combinations of two or more different halides.

The AHa and MHa are preferably substantially free of carbonaceous material, free water, and chemically combined water. satisfy these requirements and some do not. Suitable CaCl may be prepared from unsuitable reagent grade CaCl as follows: Hydrated CaCl is dried at 200 C. in

air, then is melted in a dry HCl atmosphere, and then is cooled. The solidified melt is dissolved in waterand filtered. The filtrate is evaporated and the remaining solids are dried in air at about 200 C. 1 The dry solids are remelted under a dry HCl atmosphere, and the melt solidified to produce the purified raw material. Ba'Cl and SrCl may be prepared by thev same technique. CaBr CaI BaBr Bal SrBr and SrI may be prepared by the same technique except that HBr and HI atmospheres are substituted for HCI when preparing the bromides and iodides respectively. Direct combinationof the metal and halogen can also be used as a means of Example 1.Mix 0.5 l0 mol Sm O with 1 mol pure anhydrous CaCl Melt the mixture in a dry atmosphere containing about equal parts by volume of hydrogen and HCl. The proportions in parts by volume of H /HCI may be between /10 and 20/80. Solidify the r melt by cooling to form a luminescent material having a tetragonal crystal structure and the molar formula CaCl :0.00lSm+ At liquid nitrogen temperatures and with visible 'or ultraviolet excitation, the material luminesces in narrow bands at wavelengths of about 6945 A., 7075A., and 7355 A. Q

Example 2.To prepare cubic SrCl :0.001Sm follow the procedure of Example 1 except substitute SrOl for CaCI V f Example 3. To prepare orthorhombic BaCl 0.00lSm+ follow the procedure of Example 1 except substitute BaCl for CaCl Example 4.-Mix' l.O l0 mol UF (or UO with one mol pure anhydrous BaBr Melt the mixture in a dry atmosphere containing about equal parts by volumeof hydrogen and HBr. Solidify the melt by cooling to produce luminescent material having an orthorhombic crystal structure and the molar composition BaBr :0.00lU+ With infrared, visible or ultraviolet excitation, the matei.

BaBr Melt this mixture in a dry atmosphere containing 3,163,608 Patented Dec. 29, 1964 Some reagent grade raw materialsabout equal parts by volume of hydrogen and HBr and then solidify the melt by cooling: The solidifiedmelt' is mixed with 0.50 l() mol thulium metal. This miX- ture is melted under a hydrogen atmosphere and then solidified by cooling. The productisa lumi nescent material having an orthorhombic crystal structure andthe molar composition BaBr :0.OlTm+ Example 6.-Mix 1.0x l0 mol Sm O with-one mol pure anhydrous SrCl and one mol pure anhydrous- BaCl Melt the mixture in a dry atmosphere containing about equal parts by volume of hydrogen andHCl, and thensolidify the melt by cooling. The product is a luminescent material having a cubic crystal structure and the molar formula Sr Ba C1 0.001Sm' Example 7;-Mix-' 1.0 10- mol samariu'm metal powder with one molpure barium'metal. Heat the'mixture at about 800 C. in a stream of hydrogen gas containing elemental iodine in gaseous form. At this temperature, the metal mixture reacts with the'gaseous iodine to form a-molten product. The metal mixture floats on the melt. When all of the metal is reacted; solidify the melt by cooling. Thepro'duct'is a luminescent material having an orthorhombic crystal structure and the molar composition BaI :0.001Sm+ The luminescent materials of the invention may be prepared as relatively large single crystals with a high degree of crystallinity. This may be achievedrby melting. the luminescent materials of the invention and growing, crystals thereof bythe Bridgman technique, either horizontal or vertical; The horizontal Bridgman" technique isprefrred. In one application of the Bridgman technique, a quantity ofmaterialis passed-throughitwo zones; oneof which is maintained at temperatures about C. above the meltingpoint of the material'and the". other of which is-maintained at temperatures'about: 20 C. below the melting point of the material. A. rate of travel of about one inchper- 2 1 hours through the zoneshasbeen found to be adequate. Large single crystals may also be grown by the Czochralski method.

What is claimed is:

1. A luminescent material having-'the-molar composition:

AHa zyU+ 4 where:

A is at least one materi'al'of'tlie group consisting of Ba, Ca, and S r Ha is at least one material of the group consisting of Cl, Br, and I U+ is trivalent uranium y is'between about 10" and 10* 'mol.

2. A luminescent material having the molar composition:

AHa :yU+ where:

A is one materialof the groupconsisting'of'Ba, Ga, and

Sr Ha is one material of the group consisting, of C1,,Br,

and I U is trivaleht'uranium y isbetween about 10* and 10* mol.

3.- A luminescent material having the-molar composi- 5. A luminescent material having an orthorhombic crystal structure and the-molar composition:

where y is between about 10 and 1'0- References Cited inthe file of this patent Anom: Chem. andEng. News; volE 38, No. 52; p; 39. December 26,1960. TPI14-18; V

B'at'ement: Transactions of theFara'day Society,vol, 44, page 617 (1948 V 

1. A LUMINESCENT MATERIAL HAVING THE MOLAR COMPOSITION: 